Vehicle navigation systems now provide guidance that optimizes routes as a function of travel distance. While options are sometimes given to optimize routes for travel time instead, these are generally primitive approximations based on speed limits or historical travel time data. And while a variety of traffic data sources are available, transferring the data to mobile navigation devices in a useful manner is difficult. To generate optimized routes, recent traffic flow rate data about all possible roads considered by the navigator must be available, which necessitate that transfer of large amount of data to mobile navigation devices. Traffic flow rate data can change quickly, and data that is even a few minutes out of date can cause suboptimal routes to be generated. Thus data must be transmitted frequently to keep device databases up to date.
Several approaches have been tried to optimize navigator routing for traffic information, but all have significant drawbacks. One approach taken is to transmit information via FM TMC (Traffic Message Channel through frequency modulated radio broadcasts). While this approach is inexpensive, data transmission is slow. As a result only limited information about traffic jams and traffic incidents is transmitted rather than traffic flow rate data.
Another current approach is to transmit traffic information via a wireless modem. This approach is expensive because wireless carriers must be paid for the transmission. As a result, transmitted information is often limited to information about traffic jams and traffic incidents rather than traffic flow rate data. If traffic flow rate data were to be transmitted, a significant delay would result due to the volume of data required, which is undesirable in a navigation system.